Abstract

We present a versatile terahertz time-domain spectrometer which allows reflection measurements at normal incidence and double pass transmission measurements in a single experimental setup. Two different modes for transmission measurements are demonstrated for precise measurements of transparent high or low refractive index materials, respectively. The refractive indices and absorption coefficients of cesium iodide, potassium bromide, sodium chloride, polytetrafluoroethylene (PTFE, Teflon), and silicon have been measured in the frequency range between 1.4 and 4.7 THz. The parameters of the Lorentz oscillator functions describing the phonon polariton dispersions of CsI and KBr have been determined.

Figures (6)

Experimental setup of the terahertz time-domain spectrometer for simultaneous transmission and reflection measurements: BS, beam splitter; ITO, glass plate coated with indium tin oxide; DAST, 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate crystal used as terahertz transceiver; Ge, germanium crystal. Inset: The sample holder can be moved perpendicular to the terahertz beam into three different positions. In the first position, the terahertz pulse reflected from the sample or transmitted through the sample is measured. In the second and third positions, the terahertz signal reflected from the planar mirror or from the spherical mirror is used as a reference signal for reflection or for double pass transmission measurements, respectively.

Refractive index and absorption coefficient of PTFE measured by terahertz time-domain spectroscopy in a double pass transmission configuration where the terahertz pulse is back-reflected from an external spherical mirror (see text for details).

Refractive index and absorption coefficient of silicon measured by terahertz time-domain spectroscopy in two different double pass transmission configurations (see text for details). Solid lines: the terahertz pulse is back-reflected from the rear surface of the sample. Dashed lines: the terahertz pulse is back-reflected from an external spherical mirror.